【作者】 吴迪；

【导师】 梁卫国；

【作者基本信息】 太原理工大学 ， 采矿工程， 2010， 硕士

【摘要】 我国是煤炭工业大国,煤层瓦斯资源极为丰富,但由于煤层瓦斯储层普遍属于低渗透储层,有别于美国的煤层地质条件,不能完全按照美国的煤层瓦斯开采方式进行开采。而传统的煤层气开采方法采收率低,采气时间长,经济效益差。煤层瓦斯抽采率低的直接后果是煤矿瓦斯灾害频发、采煤效率低、环境污染等。对于我国绝大多数煤层渗透率较低的特点和煤矿瓦斯抽采率低的现状,建议采用CO2驱替煤层瓦斯,以提高煤层气产气速度和采收率。二氧化碳置换驱替煤层具有CO2煤层地质储存及CH4清洁能源开采的双赢效益,被认为是有较好前景的煤层气开采技术。本文在煤体结构特征与瓦斯赋存机理研究基础上,在实验室对CH4和CO2在煤体的渗透率及二氧化碳驱替煤体瓦斯进行了试验研究。通过煤层气的储层特征及赋存、运移与产出机理。煤样CO2吸附量大于对CH4的吸附量,分析了二氧化碳驱替煤层瓦斯的机理与适用性。渗透实验结果表明:CH4在煤体中渗透率与体积应力呈负指数规律变化;煤体对二氧化碳的渗透率高于对CH4气体的渗透率2个数量级以上,在瓦斯浓度一定的情况下增加了混合气体流量,二氧化碳驱替煤层气技术可以大幅提高煤层瓦斯采收速率。采用大煤样试件进行的二氧化碳置换驱替煤层瓦斯试验,比较真实地模拟了煤层孔隙和裂隙中储存二氧化碳及其驱替煤层瓦斯的过程。置换驱替试验结果表明:随体积应力及渗透驱替压力的不同,单位体积煤体可储存17.47至28.0体积二氧化碳,CO2/CH4置换体积比高达7.03~13.91;在恒定体积应力及渗透压力条件下,二氧化碳注入、置换、产出能够平稳进行;两种不同煤层瓦斯含量条件与驱替置换方式下,产出气体初期CH4含量高达20~50%,随时间延续产出气体中瓦斯含量有所下降,但仍持续保持在10~16%之间;在二氧化碳注入煤体进行置换吸附期间,受竞争吸附及外界温度的影响,煤体孔裂隙内气体反复发生吸附解吸,引起煤体基质发生膨胀收缩;当温度变化幅度较大时,由温度升高导致的气体解吸及膨胀效应远远大于气体解吸煤体基质的收缩效应。研究结构表明,注入CO2置换驱替煤体瓦斯的主要机理为:(1) CH4与CO2的竞争吸附,由于煤体对CO2的吸附性远高于对CH4的吸附性,使得注入的CO2能够滞留,且置换出大量CH4。(2) CO2注入过程中,由于气体的渗流运移,减小了吸附CH4分压,从而使得其持续解吸;提高CH4产量。本研究对CO2在不可采煤层中地质储存及置换驱替煤层瓦斯均具有重要的理论意义与应用价值。更多还原

【Abstract】 China is a big coal industry country with very rich coal-bed methane resources, however ,coal-bed methane reservoirs are three low-permeability reservoir, which is different from the U.S coal-bed geological conditions, coal-bed methane exploitation can not fully follow the U.S. approach. The traditional coalbed methane exploitation methods are lower productivity、longer recovering period and poor economic results.The direct consequences of low recovery ratio of coal-bed methane are gas disaster-prone,inefficient mining , resources waste and environmental pollution.based on low permeability characteistic of most coal-bed and corrent ststus of low recovery ratio of coal-bed methane in china ,the corbon dioxide enhanced coal-bed methane technology has been suggested for the purpose of enhancing coal-bed mehtane recovery ratio. carbon dioxide displacement coal-bed methane is considered a better prospect coal-bed methaneexploitation technology.In this paper, mainly based on existing technologies of carbon dioxide sequestration in coal-bed and enhanced coal-bed methane production by gas injection,according to the theories of coal-bed methane geology,rock mechanics、solid mechanics、porous medium、flow mechanics in porous medium,coal-bed methane and carbon dioxide laboratory permeability tests and carbon dioxide displacement coal-bed methane tests.doing the following work: Through the understanding of coal structure,the characteistic of coal-bed methane reservoir and the mechanisms of storage、migration and production of coal-bed methane were introduced.carbon dioxide adsorption quantity is higher than coal-bed methane,analysis the mechanism and applicability of carbon dioxide displacement coal-bed methane.under the coal-bed methane and carbon dioxide permeability tests.the results show that: In the experiment, permeability of the coal specimen was measured firstly and it is found that the permeability of the specimen is different for the two gases. The permeability for carbon dioxide is larger than that for methane two magnitudes at least under the tested condition. There exists a negative exponent relationship between the permeability and applied body stress on the specimen.Improving the coal-bed methane concntration and flow rate ,the technology of carbon dioxide enhanced coal-bed methane can substantially increase the methane recovery and mining efficiency. we present our experimental study results of carbon dioxide sequestration and methane displacement by carbon dioxide in coal specimens of large size, which factually simulated the process of the green house gas sequestration and methane displacement by it in coal bed. In the experiment, permeability of the coal specimen was measured firstly and it is found that the permeability of the specimen is different for the two gases. The permeability for carbon dioxide is larger than that for methane two magnitudes at least under the tested condition. There exists a negative exponent relationship between the permeability and applied body stress on the specimen. Under the simulated stress condition in the experiment,17.47 to 28.0 units of carbon dioxide can be stored in per unit of the specimen, and the displacement ratio of carbon dioxide to methane is as large as 7.03 to 13.91. The process of injection, adsorption and desorption, displacement, and output of gases can be proceed smoothly under the given pressures, the percentage of methane in the production gas can be amounted to 20 to 50% at the early stage and still be maintained at the level of 10 to 16% even at the last stage during the experiment process. It is concluded that the production amount and the percentage of methane are determined by complex factors including contained methane and the development of pores and fissures in the coal bed, the displacement style and applied stress during the project implementation,et al. During the process of carbon dioxide injection and gas displacement,coal body swelling can happen with comprehensive effects of gas adsorption and desorption, and the deformation of coal framework. In the experiment,it is concluded that gas desorption effect resulted from temperature increase played much role on the specimen swelling than shrink effect of the coal framework.the results showed that the main mechanism of carbon dioxide displacement of coal-bed methane:(1)At the time of coal-bed methane and carbon dioxide in the competitive adsorption, due to the adsorption of carbon dioxide is much higher than on the adsorption of coal-bed methane,ingected carbon dioxide can retention in coal, and replacement of large number of coal-bed methane;(2) The process of carbon dioxide injection, because of gas seepage and migration, reduces the partial pressure of adsorption methane, allowing its continued desorption; increased methane production. This study on non-coal layer carbon dioxide geological storage and the replacement drive for coal seam gas are of great theoretical significance and application value.更多还原